Research On The Effect Of Freeze-thaw Cycle And Sulfate Erosion On The Damage Of Cement Mortar

Durability degradation of cementitious materials mainly includes sulfate erosion, freezing and thawing damage, alkali-aggregate reaction, temperature and humidity transmission and steel corrosion caused by the chlorine ion, etc. In fact, cementitious materials are not likely to be affected by a single factor, but by a variety of factors. The impact caused by the interaction of various factors on concrete structures and cementitious materials will be more complex. Therefore, it is very important to carry out the research about complex factors on the durability of cementitious materials.There are more than one thousand salt lakes in the cold area of West China, many of which are saline alkali soil, and the content of sulfate is particularly high. For the eastern coastal areas, due to the large number of sulfate ions in the sea water, plus the temperature in winter tends to be low, there will be icing. The buildings in the above two areas will also be subjected to the combined effects of sulfate erosion and freeze-thaw cycles, which have a serious impact on cementitious materials, then the cost for maintenance and repair brings great local economic pressure. Therefore, it is very necessary to study the law and mechanism of freeze-thaw cycles damage and sulfate erosion to improve the durability of cementitious materials.Since erosion and salt sulfate freeze damage is the main failure of cementitious materials in concrete, so this study choses cement mortar to replace concrete. It studied single influence of freeze-thaw cycles or sulfate erosion on the mechanical properties of cement mortar, as well as freeze-thaw cycles and sulfate erosion two-factor effects, Mass loss rate, relative dynamic elastic modulus and compressive strength were analyzed by comparing with different cementitious materials, water-cement ratio and solution concentration, and the following conclusions were drawing:(1)Under the single factor of freeze- thaw cycles, admixture of fly ash can improve frost resistance of mortar, and made mass loss rate, the relative dynamic elastic modulus and compressive strength decrease slowly at early stage; inappropriate fly ash may contribute to freeze-thaw cycles, accelerated the deterioration of the mortar at the late stage.(2)Ordinary Portland cement mortar specimens with different water-cement ratio were soaked in 5% sodium sulfate solution, as the age went, the relative dynamic elastic modulus mortar, compressive and flexural strength can be divided into two phases: strengthening stage and deterioration stage, while high sulfate resistant cement mortar can divided into the strengthening stage and the stable stage.(3)Two kinds of cement mortar with different water-cement ratio were soaked in 5% sodium sulfate solution, with the increase of the penetration depth, the content of free sulfate ion first decreases and then tended to be stable. At 180 days, sulfate ion penetration depth of ordinary Portland cement is about 7 ~ 10 mm. The content of free sulfate ion in high sulfate cement mortar was more than that of ordinary Portland cement mortar.(4)It carried out freeze-thaw cycle in different concentrations of sulfate solution for ordinary Portland cement mortar, the size of mass loss rate: the water > 5% sodium sulfate solution> 10% sodium sulfate solution. At 150 freeze-thaw cycles, ordinary Portland mortar specimens, high sulfate resistant cement mortar specimens and ordinary mortar with 20 percent fly ash had the mass loss rate of 2.83%, 1.78% and 4.8%, while strength loss rate of 40%, 34% and 60%.